Fiveable
Fiveable
start studying now
start studying now
Inorganic Chemistry I
Unit 12 Overview: Organometallic Reactions and Catalysis
12.1 Fundamental Organometallic Reactions
12.2 Homogeneous Catalysis
12.3 Industrial Applications of Organometallic Catalysts

🧶inorganic chemistry i review

12.1 Fundamental Organometallic Reactions

Last Updated on August 9, 2024

Organometallic reactions are the backbone of modern synthetic chemistry. They involve metal-carbon bonds and enable transformations impossible with organic chemistry alone. These reactions are crucial for making drugs, materials, and industrial chemicals.

Understanding fundamental steps like oxidative addition, reductive elimination, and insertion is key. These processes allow metals to activate molecules, form new bonds, and create complex structures. Mastering these reactions opens up a world of synthetic possibilities.

Fundamental Reaction Steps

Oxidative Addition and Reductive Elimination

Top images from around the web for Oxidative Addition and Reductive Elimination

  • File:Catalitic cycle for hydrogenation with Wilkinson's catalyst.svg - Wikimedia Commons View original

    Is this image relevant?

  • Category:Oxidative addition - Wikimedia Commons View original

    Is this image relevant?

  • File:Catalitic cycle for hydrogenation with Wilkinson's catalyst.svg - Wikimedia Commons View original

    Is this image relevant?

1 of 3

Top images from around the web for Oxidative Addition and Reductive Elimination

  • File:Catalitic cycle for hydrogenation with Wilkinson's catalyst.svg - Wikimedia Commons View original

    Is this image relevant?

  • Category:Oxidative addition - Wikimedia Commons View original

    Is this image relevant?

  • File:Catalitic cycle for hydrogenation with Wilkinson's catalyst.svg - Wikimedia Commons View original

    Is this image relevant?

1 of 3
  • Oxidative addition increases the oxidation state and coordination number of a metal center
    • Involves breaking of a covalent bond in a substrate and formation of two new bonds to the metal
    • Common example involves addition of H2 to square planar Pt(II) complexes, forming octahedral Pt(IV) hydride species
  • Reductive elimination decreases the oxidation state and coordination number of a metal center
    • Reverse process of oxidative addition, combining two ligands to form a new bond
    • Crucial step in many catalytic cycles (C-C bond formation in cross-coupling reactions)
  • These processes often occur as a pair in catalytic cycles
    • Oxidative addition activates substrates, while reductive elimination forms desired products

Insertion and Elimination Reactions

  • Migratory insertion combines a coordinated ligand with an adjacent ligand
    • Carbon monoxide insertion into metal-alkyl bonds forms acyl complexes
    • Alkene insertion into metal-hydride bonds (key step in olefin polymerization)
  • β-Hydride elimination removes a hydrogen atom from a carbon atom two positions away from the metal
    • Requires an empty coordination site and a β-hydrogen
    • Important in alkene isomerization and dehydrogenation reactions
  • These reactions play crucial roles in many industrial processes
    • Hydroformylation (combines insertion and elimination steps)
    • Ziegler-Natta polymerization (repeated insertions form polymer chains)

Transmetallation and Ligand Substitution

  • Transmetallation transfers an organic group from one metal to another
    • Common in cross-coupling reactions (Suzuki, Stille couplings)
    • Involves exchange between a main group organometallic compound and a transition metal complex
  • Ligand substitution replaces one ligand with another on a metal center
    • Can occur through associative, dissociative, or interchange mechanisms
    • Crucial for catalyst activation and substrate binding in many reactions
  • Both processes alter the electronic and steric properties of metal complexes
    • Fine-tuning reactivity and selectivity in catalytic systems
    • Enabling the design of specialized catalysts for specific transformations

Addition Reactions

Nucleophilic and Electrophilic Additions

  • Nucleophilic addition involves attack of a nucleophile on an unsaturated ligand
    • Common in reactions of coordinated CO, alkenes, and alkynes
    • Nucleophilic attack on coordinated CO forms metallacycles or acyl complexes
  • Electrophilic addition occurs when an electrophile attacks a metal-ligand multiple bond
    • Protonation of metal-alkyl complexes can lead to alkane elimination
    • Halogenation of metal-alkene complexes forms haloalkyl species
  • These additions often result in the formation of new organic functional groups
    • Hydrogenation of alkenes via nucleophilic addition of metal hydrides
    • Functionalization of olefins through electrophilic addition followed by reductive elimination
  • Carbene insertion involves the addition of a carbene ligand into a metal-ligand bond
    • Occurs with both Fischer and Schrock carbene complexes
    • Can lead to C-H insertion, cyclopropanation, or ylide formation
  • Carbene complexes serve as versatile intermediates in organic synthesis
    • Cyclopropanation of alkenes (Simmons-Smith reaction)
    • C-H functionalization through carbene insertion into C-H bonds
  • Related processes include nitrene and oxene insertions
    • Nitrene insertion used in aziridination and C-H amination reactions
    • Oxene insertion important in epoxidation and hydroxylation processes

Activation and Rearrangement Processes

Cyclometallation and C-H Activation

  • Cyclometallation forms a metallacycle through C-H bond cleavage
    • Often occurs with nitrogen-containing ligands (phenylpyridines)
    • Results in formation of stable five- or six-membered metallacycles
  • C-H activation directly cleaves and functionalizes typically unreactive C-H bonds
    • Can occur through various mechanisms (oxidative addition, σ-bond metathesis)
    • Enables late-stage functionalization of complex molecules
  • Both processes allow for selective functionalization of organic compounds
    • Cyclometallation used in the synthesis of organometallic luminescent materials
    • C-H activation applied in the synthesis of pharmaceuticals and agrochemicals
  • Metathesis involves the exchange of atoms or groups between two molecules
    • Olefin metathesis exchanges carbene units between alkenes
    • Alkyne metathesis forms new carbon-carbon triple bonds
  • Various types of metathesis reactions exist
    • Ring-closing metathesis forms cyclic compounds from acyclic dienes
    • Cross-metathesis combines two different alkenes to form a new alkene
  • Metathesis reactions have revolutionized organic synthesis
    • Enable the construction of complex molecular architectures
    • Used in the production of pharmaceuticals, polymers, and fine chemicals
  • Related rearrangements include σ-bond metathesis and α-elimination
    • σ-bond metathesis exchanges ligands without changing metal oxidation state
    • α-elimination forms metal-carbene complexes from alkyl ligands

Key Terms to Review (28)

Coordination number: The coordination number refers to the total number of ligand atoms that are directly bonded to a central metal ion in a coordination complex. This number plays a crucial role in determining the geometry and properties of the complex, influencing how it interacts with other molecules and its overall stability.
C-H Activation: C-H activation is a chemical process that involves the conversion of a carbon-hydrogen (C-H) bond into a carbon-metal bond, allowing for further functionalization of organic molecules. This transformation is significant in organometallic chemistry, as it enables the direct modification of hydrocarbons and can lead to the development of new synthetic pathways, increasing the versatility of organic synthesis. C-H activation is pivotal for forming new chemical bonds and expanding the reactivity of otherwise inert C-H bonds in various compounds.
Carbene Insertion: Carbene insertion refers to a fundamental organometallic reaction where a carbene, a species containing a neutral carbon atom with two non-bonding electrons, inserts into a metal-ligand bond. This process allows for the formation of new carbon-carbon or carbon-metal bonds, making it a valuable tool in organic synthesis and catalysis. Carbene insertions can occur with various metals and lead to the production of diverse organic compounds.
Cyclometallation: Cyclometallation is a fundamental organometallic reaction that involves the formation of a cyclic complex by the coordination of a metal to a ligand, typically through a C-H bond activation. This reaction often results in the formation of a stable, five- or six-membered ring structure, where the metal atom becomes part of the ring. Cyclometallation plays a crucial role in the development of new catalysts and materials in organometallic chemistry.
Metathesis: Metathesis is a chemical reaction where two compounds exchange components to form two new compounds, effectively swapping their parts. This process is often facilitated by catalysts, particularly in organometallic chemistry, and plays a crucial role in synthesizing a variety of organic and inorganic compounds.
Nucleophilic addition: Nucleophilic addition is a chemical reaction where a nucleophile attacks an electrophile, leading to the formation of a new covalent bond. In the context of organometallic chemistry, this type of reaction is significant for forming carbon-metal bonds and enables the synthesis of various organic compounds by introducing nucleophiles to electron-deficient carbon centers.
Electrophilic addition: Electrophilic addition is a chemical reaction where an electrophile reacts with a nucleophile, resulting in the formation of a new bond. This reaction is significant in organometallic chemistry as it allows for the incorporation of new groups into organic molecules, often altering their reactivity and properties. Electrophilic addition plays a vital role in synthesizing various compounds by facilitating the transformation of alkenes and alkynes through interactions with electron-rich species.
Ligand substitution: Ligand substitution is a fundamental reaction process in coordination chemistry where one ligand in a metal complex is replaced by another ligand. This process can alter the properties of the metal complex, affecting its reactivity, color, and stability. Understanding ligand substitution is crucial for manipulating coordination compounds in various chemical applications, including catalysis and material science.
Transmetallation: Transmetallation is a fundamental organometallic reaction where a metal complex exchanges its metal center with another metal, resulting in the formation of new metal complexes. This process often involves the transfer of a ligand from one metal to another and is crucial in the synthesis of various organometallic compounds, facilitating transformations in catalytic processes.
Migratory insertion: Migratory insertion is a fundamental organometallic reaction where a metal complex reacts with an unsaturated organic molecule, resulting in the migration of a ligand or substituent to a new position within the metal coordination sphere. This reaction is critical for the formation of new carbon-metal bonds and often occurs in catalytic processes, highlighting its importance in synthetic chemistry.
Henry Taube: Henry Taube was a renowned American inorganic chemist, celebrated for his pioneering work in the field of electron transfer reactions in coordination compounds. He is particularly recognized for elucidating the mechanisms of redox reactions and developing the concept of inner and outer sphere electron transfer, which are fundamental in understanding organometallic reactions and their pathways.
Georg Wittig: Georg Wittig was a German chemist best known for his invention of the Wittig reaction, a fundamental organometallic reaction that allows for the synthesis of alkenes by reacting aldehydes or ketones with phosphonium ylides. His work significantly advanced the field of organic synthesis and organometallic chemistry, influencing both academic research and industrial applications in catalyst development and pharmaceutical production.
β-hydride elimination: β-hydride elimination is a fundamental organometallic reaction where a metal complex eliminates a hydrogen atom and a ligand, typically resulting in the formation of an alkene. This reaction occurs when there is a β-hydrogen atom adjacent to the metal center, and it plays a crucial role in the behavior of transition metal complexes. Understanding this process helps explain how certain metal complexes can undergo transformations that lead to product formation or changes in coordination environments.
Cross-coupling reactions: Cross-coupling reactions are powerful synthetic methodologies that involve the joining of two different organic fragments, typically mediated by a transition metal catalyst. These reactions allow for the formation of new carbon-carbon or carbon-heteroatom bonds, enabling the construction of complex molecular architectures. They are widely used in organic synthesis, particularly in the pharmaceutical and materials industries, due to their ability to create diverse compounds efficiently.
Temperature dependence: Temperature dependence refers to how the rate and equilibrium of chemical reactions change with variations in temperature. This concept is crucial as it influences reaction kinetics, thermodynamics, and can significantly affect the stability and reactivity of organometallic compounds during fundamental reactions.
Carbene ligands: Carbene ligands are neutral species characterized by a divalent carbon atom with only six valence electrons, resulting in a carbon atom that has an empty p-orbital. These unique ligands can stabilize metal complexes and participate in various organometallic reactions due to their ability to form strong bonds with metal centers. They can exist in two forms: singlet and triplet, which significantly influences their reactivity and interactions with metal centers.
Solvent effects: Solvent effects refer to the influence that the choice of solvent has on the reactivity, selectivity, and overall outcome of chemical reactions. This term is particularly relevant in organometallic chemistry, where solvents can stabilize or destabilize intermediates and transition states, affecting reaction mechanisms and product distributions.
Insertion Reactions: Insertion reactions are a type of chemical reaction in which a molecule is added to a metal complex, resulting in the formation of new bonds and often leading to the creation of new molecular structures. These reactions are crucial in organometallic chemistry as they can modify metal-ligand interactions and influence the reactivity of the complex, allowing for the synthesis of a variety of organic compounds through coordination with unsaturated substrates.
Phosphine ligands: Phosphine ligands are a class of organophosphorus compounds characterized by the presence of phosphorus atoms bonded to one or more organic groups. These ligands are important in coordination chemistry and organometallic chemistry due to their ability to stabilize metal centers and influence the reactivity of metal complexes through their electron-donating properties.
Reductive Elimination: Reductive elimination is a fundamental organometallic reaction where a complex, typically containing a metal center with two different ligands, forms a product by eliminating those ligands in a coupled manner. This reaction is crucial because it helps in regenerating the metal center in a lower oxidation state and often leads to the formation of new carbon-carbon or carbon-heteroatom bonds, which is essential in synthetic organic chemistry.
σ-bond metathesis: σ-bond metathesis is a fundamental organometallic reaction where two σ-bonds are broken and reformed, typically involving the exchange of ligands between metal centers. This reaction allows for the rearrangement of bonds without requiring a complete cleavage of the molecule, facilitating the transformation of reactants into products. It's essential in the development of various catalytic processes and in the synthesis of complex molecules.
Oxidative Addition: Oxidative addition is a fundamental reaction in organometallic chemistry where a metal complex reacts with a substrate, resulting in the increase of the oxidation state of the metal and the formation of new bonds. This process typically involves the addition of two ligands to the metal center, which can enhance catalytic activity and facilitate further transformations. The reaction is crucial in processes such as homogeneous catalysis, allowing for the activation of substrates and facilitating subsequent chemical reactions.
Aryl metal: Aryl metal refers to organometallic compounds that contain a metal atom bonded to an aryl group, which is a functional group derived from an aromatic ring. These compounds are important in various chemical reactions, particularly in forming carbon-carbon bonds and as intermediates in organic synthesis, highlighting their relevance in fundamental organometallic reactions.
Alkyl metal: An alkyl metal is a type of organometallic compound where an alkyl group is bonded to a metal, typically an alkali or alkaline earth metal. These compounds are significant in various fundamental organometallic reactions, serving as strong nucleophiles that can react with electrophiles to form new carbon-carbon bonds. They play a crucial role in synthesis, polymerization, and in facilitating reactions that involve the transfer of alkyl groups.
Electrophilicity: Electrophilicity is the property of a chemical species that makes it an electron-deficient atom or molecule, which seeks to accept electrons from a nucleophile during a chemical reaction. This characteristic plays a critical role in determining how molecules interact and react with one another, especially in organometallic compounds where metals often serve as electrophiles. Understanding electrophilicity is essential for predicting reaction mechanisms and the types of products formed in organometallic chemistry.
Nucleophilicity: Nucleophilicity refers to the ability of a chemical species to donate an electron pair to an electron-deficient center, typically in the context of a chemical reaction. This property is essential in organometallic chemistry, where nucleophiles interact with electrophilic centers in metal complexes, influencing the reaction pathways and outcomes. Understanding nucleophilicity helps explain how different organometallic compounds can behave in various reactions, especially those involving bond formation and breaking.
D-block elements: D-block elements are the transition metals found in groups 3 to 12 of the periodic table, characterized by the filling of d orbitals. These elements exhibit unique properties such as variable oxidation states, complex ion formation, and catalytic activity due to their ability to lose different numbers of electrons from their d orbitals.
Catalysis: Catalysis is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst, which remains unchanged after the reaction. Catalysts work by lowering the activation energy required for a reaction to proceed, making it easier for reactants to convert into products. This phenomenon plays a significant role in both inorganic polymers and clusters, as well as fundamental organometallic reactions, facilitating transformations that are often critical for industrial and synthetic processes.
Back
Glossary
12.2 Homogeneous Catalysis